1. Field of the Invention
The invention relates to a method for transmitting three data signals of a USB signal in which the first data signal is transmitted differentially via a first conductor pair and the second data signal is transmitted differentially via a second conductor pair. The invention also relates to a system for transmitting USB signals and an adapter for such a system.
2. Description of Related Art
Conventional USB2 interfaces (for example USB 2.0 interfaces) have a signal conductor pair (D+ and D−) and a conductor pair for the power supply (GND, VBUS). The data transmission takes place symmetrically and bi-directionally via the signal conductor pair, whereby the data signal (“signal portion”) is transmitted through one conductor of the signal conductor pair and the corresponding inverted data signal (“reference portion”) is transmitted through the other conductor. For this purpose a cable designed for the transmission of USB2 signals has, as a signal conductor pair, two twisted and shielded conductors in order as far as possible to avoid transmission interference. The signal receiver forms the differential voltage of the data signal transmitted via the signal conductor pair differentially (namely symmetrically), so that interference affecting both conductors of the signal conductor pair equally is eliminated.
The transmission of USB signals is necessary in an extremely wide variety of technical applications. For example, a USB socket can be required in a rear section of a vehicle in order to allow USB devices to be plugged in, so that a USB cable needs to be passed through the vehicle from the front to the rear. USB sockets or USB connections can also be required in various locations (offices, public facilities, means of transport, etc.) for the connection of USB devices, whereby USB cables need to be laid for this purpose. As explained above, two conductor pairs are sufficient for the transmission of a conventional USB2 signal (data signal and supply voltage), so that four-wire cables were formerly laid for the transmission of USB signals.
A few years ago, the USB3 standard was introduced. USB3 interfaces (for example USB 3.0 interfaces) have, in addition to the aforementioned connections (D+, D−, GND, VBUS), at least two additional signal conductor pairs (SSTX+ and SSTX−; SSRX+ and SSRX). A differential data signal is transmitted or fed into the USB interface via each of these two signal conductor pairs. Overall, this allows higher data rates to be achieved than with the conventional USB2 standard.
Consequently, in order to achieve USB3 compatibility, new plug connectors on the host and on the connected devices and additional data transmission cables are necessary. For this purpose, a further four-wire cable was laid for the transmission of USB3 signals, whereby the aforementioned eight USB3 connections (D+, D−, GND, VBUS, SSTX+ and SSTX−; SSRX+ and SSRX−) are then transmitted via two four-wire cables. The total of three data signals are thereby transmitted differentially via in each case one conductor pair (D+ and D−; SSTX+ and SSTX−; SSRX+ and SSRX−). However, the laying of additional cables involves considerable expense.
Alternatively, instead of the two four-wire cables, it is naturally possible to lay a single standard USB3 cable. However, laying such a cable involves even greater expense, since the old USB2 cables need to be removed and the new USB3 cables are expensive.